Filled reaction tube provided with temperature sensors

ABSTRACT

A catalyst-filled reaction tube provided inside with several temperature sensors, and the insertion of electric leads and their protecting tubes in axial recesses in the tube wall (which may be homogeneous or consist of several layers) without making holes in the tube wall.

United States Patent Friedrichsen et 'al.

[54] FILLED REACTION TUBE PROVIDED WITH TEMPERATURE SENSORS [72]inventors: Wilheim Friedrichsen; Guenter Poehler;

Gert Goeschel, all of Ludwigshafen; Gerhard Schaefer, Limburgerhof, allof Germany Badische Anilin- & Soda-Fabrik Aktiengesellschaft,Ludwigshafen, Rhine, Germany [22] Filed: Mar. 13,1970 [21] App1.No.:19,420

[73] Assignee:

[30] Foreign Application Priority Data Mar. 15, 1969 Germany ..P 19 13267.3

[52] U.S. Cl...., ..23/288M,73/341,138/111 [51] Int.Cl...B0lj9/04,G0lk1/08,G01k1/14 [58] Field of Search ..73/340, 341, 342,343 R; 23/288, 288 H, 288 J, 288 K, 288 L, 288 M, 289,

[15] 3,656,914 1 Apr. 18, 1972 [56] References Cited UNITED STATESPATENTS 3,334,973 8/1967 Goren et a1. ..23/253 R 2,148,706 2/1939 Morrow..73/343 3,172,832 3/1965 Dreyer et a1. ...23/288 X 1,851,999 4/1932Black ...23/288 M UX 1,890,435 12/1932 Krauch et al ..23/288 UX NFOREIGN PATENTS OR APPLICATIONS 385,781 1/1933 Great Britain ..23/289Primary Examiner-Joseph Scovronek Attorney-Johnston, Root, OKeeffe,Keil, Thompson & Shurtleff [57 ABSTRACT A catalyst-filled reaction tubeprovided inside with several temperature sensors, and the insertion ofelectric leads and their protecting tubes in axial recesses in the tubewall (which may be homogeneous or consist of several layers) withoutmaking holes in the tube wall.

5 Claims, 4 Drawing Figures PATENTEDAPR 18 I972 3656,91 1 SHEET 10F 2INVENTORS:

WILHELM FRIEDRICHSEN GUENTER POEHLER GERT SC GERH SC FER PATENTED RBIBZB v 3,656,914 SHEET 2 0F 2 INVENTORS:

WILH ELM FRIED RICHSEN GUEN ER PQEHLER GERT GOESCHEL GERHARD SCHAEFERFILLED REACTION TUBE PROVIDED WITH TEMPERATURE SENSORS The inventionrelates generally to tubes and tube bundles provided with temperaturemeasuring devices, and in particular to temperature sensors incatalyst-filled tubes which are surrounded by a corrosive medium.

It is known from Chemie-Ingenieur-Technik, 1964, page 327 ff., formeasuring the axial distribution of temperature in a packed columnthrough which a gas-stream is being passed, to distribute a large numberof temperature sensors over the length of the column and additionally,in specific cross-sectional planes of the packed column, to arrangeseveral tem perature sensors at difi'erent distances from the tube wallsto determine the temperature distribution over the cross-section of thetube.

Thermocouples may be used as temperature sensors; their hot junctionslocated inside the tube, that is to say on the inner surface of the tubewall. The protection tubes of the thermocouples are situated on theoutside of the tube, so that the protecting tubes are introducedradially through holes in the tube wall, which are plugged bythermocouple holders (made of special material), asbestos packing andclamping means.

In the carrying out of strongly exothermic or endothermic catalyticreactions in tubular reactors, the tubes filled with catalysts aresurrounded by a special heat-transfer medium, in special processes forexample with a salt melt. Commercial tubular reactors may have five to15,000 catalyst tubes.

In reactors whichrequire an exact temperature regime or when usingheat-sensitive catalysts, it is particularly important to know exactlythe temperature in the catalyst layer, so as to control the reactor inrespect of the optimum supply of heattransfer medium surrounding thetubes, and to be able to maintain the temperature within narrow limits.It is already known to provide one or more catalyst-filled tubes of areactor with thermocouples, to the junctions of which the thermoelectricwires run in impact-resistant reinforced protecting tubes which arearranged in the region of the axis of the reactor tube. It has beenfound that accurate temperature measurement is not possible owing to thefact that measuring tubes, in contrast to normal tubes, are filled withcorrespondingly smaller amounts of catalyst and owing to the fact thatthe catalyst is distributed differently around the sensor protectingtube.

If one selects measuring tubes of greater diameter to compensate for thedifference in quantity of the catalyst, the resultant differentcross-sectional distribution. of the catalyst does not give temperaturevalues comparable with those in a normal tube either.

Moreover, radial introduction of the sensor protection tubes through thewall of the tube is not feasible, because this does not ensure permanentand secure closure of the necessary wall openings on account of thesalt-melt which surrounds the tubes and serves as heat-transfer medium.

It is an object of this invention to provide with temperature sensors areaction tube to be filled with replaceable catalyst so that themeasured values accurately reflect the temperature distribution in tubesnot provided with sensors and to do this without perforating the tubewalls.

This object is achieved in accordance with this invention by arrangingthe leads to the temperature sensors in substantially axial recesses inthe inner wall of the tube and arranging the hot ends of the leads sothat they protrude substantially radially from the recesses towards theaxis of the tube to reach predetermined measuring points located in thefree cross-section of the tube, the depth and width of the recesses inthe tube'being at least equal to the diameter of the sensor protectingtube so that the entire free cross-section of the tube is, apart fromthe protruding ends, available for receiving the catalyst charge.

According to another embodiment of the invention such a catalyst tube isdouble-walled and has been made in several stages. In the outer wall ofthe inner tube, slots are milled running from the end of the tube to theregion of the measuring plane advantageously in a longitudinal directionand, in

which the sensor protection tubes are inserted, and this inner tubeprovided with the temperature sensors is inserted into an outer tube,with or without an intemtediate bonding layer.

Further features will be evident from the following description withreference to the drawings.

FIG. 1 shows the design of a homogeneous or one-walled reaction tube incross-section, and

FIG. la the corresponding longitudinal section along the line A B;

FIGS. 2 and 2a show the corresponding sections of a double-walledreaction tube.

To avoid changing, over major axial regions, the tube crosssectionavailable for the catalyst charge in the tube and to ensure evendistribution of the catalyst particles, axial grooves 2 are milled inthe walls of the tube, for accommodating temperature sensors, the depthand width of these grooves being at least as great as, and preferablygreater than, the diameter of the sensor protecting tubes 3. The breadthof the grooves near the inner wall of the tube may be smaller than thatnear the bottom of the grooves. They may have a partly rounded, e.g.,half-round, cross-section or have undercut edges or a trapezium-shapedcross-section formed by a dovetail groove cuttenAfter insertion of thesensor protecting tubes into these grooves, the edges of the grooves canbe shaped by means of a tool inserted under pressure into the interiorof the tube so that they keep the protecting tubes in position. It isalso possible to fix the protecting tubes in the grooves byspring-loaded rings forced into the interior of the reaction tube. Inthe simplest case the recesses 2 are prepared over the whole length ofthe tubes during manufacture of the latter. It is preferred, however,that they extend from one end of the tube to not further thanthe regionof the plane of the respective temperature sensor. In the region of thismeasuring plane, the free ends of the temperature sensors (the hotjunctions in the case of thermocouples) together with the protectingtube are bent out of the recesses 2 towards the axis into the freecross-section of the tube preferably to make an angle a of to C with thedirection in which the catalyst particles are subsequently introduced(see FIGS. 1a and 2a).

In the arrangement using double-walled tubes illustrated in FIGS. 2 and2a, the grooves 2 extend right through the thickness of the inner tube,running from the end of the tube to the region of the desired plane ofmeasurement. In the cloven inner tube In the set of temperature sensorsis inserted and wedged in position by support members or soft metal.Then the outer tube 1b which has been heated to a temperature higherthan the highest reaction temperature in use, is fitted over the innertube so that it shrinks tightly onto the latter.

In a modified method of preparing such a tube heat conduction throughthe walls of the tube can be improved simply by laying on, or wrappingaround, the inner tube 1a a sheet of readily fusible metal, over whichthe outer tube is drawn. By heating the two tubes to a temperature abovethe melting point of the metal of the interlayer, a good heat-conductingbond is obtained. Finally, it is also possible to make an intimateconnection between the two tubes of the double-walled tube, beforebending up the measuring ends (hot junctions) of the temperature sensorsout of the grooves, by means of expanding the inner tube, e. g., byforcing a sphere or other body through it.

With the reaction tubes described above it is possible to monitor thecourse of the temperature right inside the catalyst charge oflarge-scale tubular reactors, for example in reactors with a marked hotspot which can arise for example during the oxidation of varioushydrocarbons such as o-xylene or naphthalene.

We claim:

1. In a reaction tube for a tubular reactor containing a catalystpacking and being provided with temperature sensors arranged in theinterior of said packing, said sensors being located at points which aredistributed at intervals over the length of the reaction tube with theirmeasuring ends being located at a predetermined distance radiallyinwardly from the inner wall of the reaction tube, the improvement ofelectrical leads to each temperature sensor enclosed within a sensorprotecting tube which is attached to an axial recess running along thewall of the reaction tube with the hot ends of the leads together withsaid sensor being arranged to protrude from said recess towards the axisof the reaction tube to reach the predetermined measuring point in thefree cross-section of the reaction tube.

2. A reaction tube according to claim 1 in which the depth and width ofthe recesses in the wall of the reaction tube are at least equal to thediameter of the sensor protecting tube.

3. A reaction tube according to claim 1 in which the width of therecesses increases in the direction from the inner towards the outerwall of the reaction tube.

4. A reaction tube according to claim 1 which is doublewalled to providean outer tube fitted over an inner tube with slots which run from oneend of said inner tube only to the region of the measuring point in anaxial direction, into which slots the protecting tubes of thetemperature sensors are inserted.

5. A reaction tube according to claim 4, wherein said outer tube isbonded to said slotted inner tube by a heat-conducting interlayer havinga significantly lower melting point than the material of the inner tube.

2. A reaction tube according to claim 1 in which the depth and width ofthe recesses in the wall of the reaction tube are at least equal to thediameter of the sensor protecting tube.
 3. A reaction tube according toclaim 1 in which the width of the recesses increases in the directionfrom the inner towards the outer wall of the reaction tube.
 4. Areaction tube according to claim 1 which is double-walled to provide anouter tube fitted over an inner tube with slots which run from one endof said inner tube only to the region of the measuring point in an axialdirection, into which slots the protecting tubes of the temperaturesensors are inserted.
 5. A reaction tube according to claim 4, whereinsaid outer tube is bonded to said slotted inner tube by aheat-conducting interlayer having a significantly lower melting pointthan the material of the inner tube.